1. Field of the Invention
This invention relates to control devices which communicate pressure in fluid devices.
2. Description of the Related Art Including Information Disclosed Under 37 CFR .sctn..sctn.1.97-1.98
This invention relates to devices intended to communicate pressure in fluid pressure operated device. Thus, this invention applies to devices intended to transmit liquid or gas pressure, control the flow of liquids in hydraulic systems, prevent the extensive loss of liquids or gases in ruptured hydraulic or gaseous systems, and transmit pressure of liquids, solids, or gases to such liquid or gas operated instruments as pressure gauges, indicators, recorders, pressure transmitters, flow valves, or the like.
3. Description of the Related Art
Controlling the flow or pressure of liquid in hydraulic systems can be troublesome. This may be particularly observed in systems in which a diaphragm is used to transmit the pressure exerted by some media (which may be a gas, liquid, or solid) to a liquid controlled instrument (such as a pressure gauge). In these systems, a diaphragm is secured within a housing cavity. The diaphragm divides the cavity into two separate chambers. The media (or so-called process media) communicates with the diaphragm through a port in the housing into one chamber. The other chamber is filled with a liquid and secured to and communicates through a port to the pressure measuring instrument. The pressure exerted by the process media may be transmitted to this so-called "solid filled" liquid system. Thus, systems of this type are generally referred to as solid (i.e., liquid) filled diaphragm seals. The most difficult problem faced in such systems is the maintenance of the integrity of the diaphragm. If the pressure is somehow lost on the instrument side, the process media may then exert too great a pressure upon the diaphragm, and the differential pressure will exceed the diaphragm spring rate, and the diaphragm will become distorted and the measuring accuracy of the diaphragm seal is lost. In addition, a diaphragm is distorted may, as a result, become ruptured, resulting in the loss of liquid fill and possible contamination of either the measuring instruments or the process media.
A number of devices have been suggested to overcome these problems. Thus, Bissell et al., in U.S. Pat. No. 3,202,063, suggests a diaphragm capsule or unit which comprises a backing member or plate having a rigid axial hub portion permanently united or welded to a diaphragm. The backing member and the diaphragm have corresponding corrugations or convolutions so as to provide a matching seat for the diaphragm to prevent distortion in the event of the loss of fill. This arrangement requires the special manufacture of a removable unit insertable within the housing cavity. The axial stem is provided with an O-ring, the seating of which must be done with precision. Furthermore, it is necessary to match the convolutions or corrugations of the back plate with the diaphragm corrugations.
Still another device has been suggested by Green, in U.S. Pat. No. 2,841,984, in which the corrugations or convolutions of the diaphragm are matched by corrugations in the housing wall itself. Here again, there is a problem of assembly including the matching of the convolutions.
Still another device which used a matching convolution in the diaphragm with those of the housing was taught by Bailous et al., in U.S. Pat. No. 2,833,995.
Still another approach was suggested by Hailer et al. in U.S. Pat. No. 2,667,184, in which two conduit members, for transmitting hydrostatic pressure, include flexible diaphragms covering each end and joined together to form the housing cavity with the two chambers. In this arrangement, the diaphragms abut, one another, thereby sealing the line, but transmitting the hydrostatic pressure. However, because of the necessity of two abutting diaphragms, the diaphragms that are made of metal must be extremely thin and flexible or made of a rubber-lie material. The interconnecting conduits are specified by Hailer et al. to be capillary in form and not adaptable to general hydraulic systems requiring large displacement of liquid and, in particular, those intended to measure the pressure of process media. Hailer et al. also suggests the use of a bleed port at the periphery of the cavity. However, common to other devices herein, if located immediately adjacent to the periphery, the diaphragm would become damaged.
Yet another approach is disclosed in Martin, U.S. Pat. No. 2,317,073. In Martin a bladder or cup 35 is within a housing 18. Liquid is disposed between the cup 35 and the interior wall 20 of the housing 18. As pressure upon the cup 35 increases from the process side of the housing, the cup distends and drives out all of the liquid through a bore or aperture 20. There is no teaching of the entrapment of any liquid in the housing to cushion or protect the cup 35.
Thus, the existing solutions to differential pressure placed upon a flexible diaphragm have been to either double-seal the chamber with matching facing diaphragms, thereby limiting the sensitivity and not inhibiting the possibility of rupture, or to match the convolutions of a more rigid diaphragm with the convolutions in the housing or those of a removable capsule to which thee diaphragm is sealed. These latter arrangements introduce the problem of accurate alignment and assembly. The solution to the problems of diaphragm distortion due to loss of fill has led to an inventive device which is, in turn, applicable to devices having a wider area of usage as more generally referred to hereinabove.